| Abstrakt: |
Abstract Temporal–spatial distributions of nitrogen in the low-precipitation headwater areas of the Sanuki Mountain Range, Kagawa Prefecture, Japan, was studied to clarify the natural loading from forests to rivers as basic knowledge for elucidating the eutrophication in dead-water regions downstream. The survey to clarify temporal variations was carried out once every two weeks at the headwaters of five rivers in the Sanuki Mountain Range and the Shikoku Mountains on Shikoku Island, Japan, between May 6, 2002, and April 22, 2003. The survey to clarify the spatial distribution was carried out at 23 stations on the headwaters of the Sanuki Mountain Range between August 13 and 15, 2002. In the Kazuratani and Tarobei Rivers, which originate in the Sanuki Mountain Range, where precipitation is scarce, total N was consistently high – greater than 1?mg?l-1 throughout the year. The maximum value of total N was 3.2?mg?l-1 in the Kazuratani River. The spatial distribution of total N in the headwater areas was 0.47–3.8?mg?l-1. High concentrations over 1?mg?l-1 were found in the central region of the Sanuki Mountain Range and the maximum value was 3.8?mg?l-1. From these results, it became clear that nitrogen concentrations in headwater areas of the Sanuki Mountain Range are high compared with those in other regions. Various factors were considered in relation to low precipitation and drying as the causes of the high nitrogen concentrations. Furthermore, It was noted that the majority of the regions with the highest NO3--N concentrations in our study were composed of granitic rock. |
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